1. Field of the Invention
The present invention relates to a battery case for containing battery modules of an electric vehicle which runs by means of a motor using a battery as a power source.
2. Description of the Related Art
A battery unit used for an electric vehicle includes battery modules and a battery case for containing the battery modules. An example of the battery case includes a tray member for supporting the battery modules, and a cover member for covering an upper part of the tray member.
In, for example, Jpn. Pat. Appln. KOKAI Publication No. 8-186390, a tray member and cover member are disclosed. A joint part between a peripheral edge part of the tray member and peripheral edge part of the cover member is fastened by a plurality of bolts and nuts. These bolts are inserted into bolt inserting holes formed in the peripheral edge part of the cover member from above the cover member. Further, these bolts are screwed into the nuts arranged on the underside of the peripheral edge part of the tray member.
In a battery unit requiring a high degree of waterproof property such as a lithium ion battery, the joint part between the peripheral edge part of the tray member and the peripheral edge part of the cover member is provided with a waterproof seal member. Water is prevented from entering inside from the joint part by the seal member. The seal member is, for example, a resin-based seal member having fluidity, and hardens after being applied to the joint part.
In the case where the nuts are embedded in the tray member, when the liquid seal member is applied to the joint part of the tray member, part of the seal member enters the threaded part of the nut of the tray member in some cases. When the seal member enters the threaded part and hardens, there is the possibility of the tightening torque of the bolt screwed into the nut becoming unstable. In the battery case requiring a high degree of waterproof property, it is necessary to carry out torque control of bolts for fastening the tray member and cover member to each other. However, if the seal member enters the threaded part of the nut as described above, the tightening torque of the bolt is affected by the seal member, and thus accurate torque control cannot be expected.
It has been conceivable, in order to prevent the seal member from entering the threaded parts of the nuts, that embedded bolts are provided on the tray member side, and the nuts are screwed onto the bolts from above the cover member. However, in order to provide the tray member with a plurality of embedded bolts, it is necessary to attach a plurality of embedded bolts to an insert member at predetermined positions by welding or the like. Further, it is necessary to form holes into which the embedded bolts are to be inserted inside a mold die for molding the tray member.
There is naturally a limit to manufacturing an insert member of sheet metal with a high degree of accuracy. Thus, when a plurality of embedded bolts are fixed to one insert member, relative positions of the embedded bolts are somewhat deviated from ideal positions in whatever way in some cases. In the die for molding the tray member, a plurality of holes into which the plurality of embedded bolts are to be inserted are formed. Thus, if the positions of the embedded bolts are deviated even a little, it becomes difficult to insert the embedded bolts into the holes formed at predetermined positions of the die.